Soil influences wine by impacting the development of the grapes from which wine is made. Thinking of starting a vineyard in your backyard? If so, the good news is that wine grapes can grow in a diverse variety of soils, including volcanic, calcareous (a combination of calcium carbonate, limestone and seashell fossils), clay, and loam (a combination of sand, silt and clay). But if you want to grow great wine grapes, there are some soil characteristics that are particularly important. So before you plant that first vine—or if you don’t plan to plant anything at all, but just want to know more about how soil impacts wine—here’s a quick rundown of the “soil traits” that produce great wine grapes…
Soil structure is the most important factor—specifically the ability to effectively drain water. A vine with deep roots can better survive temperature extremes, and good drainage ensures that the roots make their way deep into the ground to find a stable source of water and nutrients. Drainage is influenced by the presence of rocks, gravel, sand, silt and organic matter, as well as the geologic formation of the land.
The amount of rock in soil also influences grape development. During the day, high rock-content soils reflect heat back to the vines, and at night, heat stored in the soil keeps plant roots warmer and can help continue to ripen the grapes. Soils such as clay, that are low in rock content, can slow grape maturation because they tend to retain water and remain cool, even in warm weather. Soil color also influences the ability to reflect sunlight back towards the vines and can positively impact grape development. For example, in France’s Champagne region, ripening grapes benefit from the sun reflecting off the white chalky soil.
Grape vines are nourished by the organic and mineral composition of soil. Paradoxically, soil of lower fertility is better for the production of good wine, and many fine vineyards are located on land which is not fertile enough to support many other crops. Very rich soil can lead to excessive leaf growth which diverts energy away from grape development and shields grapes from the sun, hampering their ability to ripen. It can also result in the production of “too many” grapes. Fewer grapes mean higher quality grapes because the plant’s resources are not diluted among a large number of grapes.
The PH level of the soil and the presence of metallic compounds (such as iron) are also important as they influence tannins and the acidity of the wine ultimately produced.
Clearly, one of wine’s most wonderful qualities is the way it reflects so much about the place where it was produced—soil included.